This section is intended to provide a background to the various embodiments of the technology that are described in this disclosure. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not necessarily prior art to the embodiments of this disclosure and is not admitted to be prior art by the mere inclusion in this section.
Radio communication networks are widely deployed to provide various communication services such as telephony, video, data, messaging, broadcasts, and so on. Such communication networks support communications for multiple user equipments (UEs) by sharing the available network resources. One example of such a network is the Universal Mobile Telecommunications System (UMTS), a third generation (3G) mobile phone technology standardized by the 3rd Generation Partnership Project (3GPP). UMTS includes a definition for a Radio Access Network (RAN), referred to as UMTS Terrestrial Radio Access Network (UTRAN). The UMTS, which is the successor to Global System for Mobile Communications (GSM) technologies, supports various air interface standards, such as Wideband-Code Division Multiple Access (W-CDMA), Time Division-Code Division Multiple Access (TD-CDMA), and Time Division-Synchronous Code Division Multiple Access (TD-SCDMA). The UMTS also supports enhanced 3G data communications protocols, such as High Speed Packet Access (HSPA), which provides higher data transfer speeds and capacity to associated UMTS networks. As the demand for mobile broadband access continues to increase, research and development continue to advance the UMTS technologies not only to meet the growing demand for mobile broadband access, but to advance and enhance the user experience with mobile communications. For example, third-generation UMTS based on W-CDMA has been deployed in many places of the world. To ensure that this system remains competitive in the future, 3GPP began a project to define the long-term evolution of UMTS cellular technology. The specifications related to this effort are formally known as Evolved UMTS Terrestrial Radio Access (E-UTRA) and Evolved UMTS Terrestrial Radio Access Network (E-UTRAN), but are more commonly referred to by the name Long Term Evolution (LTE). More detailed descriptions of radio communication networks and systems can be found in literature, such as in Technical Specifications published by, e.g., the 3GPP. The core network (CN) of the evolved network architecture is sometimes referred to as Evolved Packet Core (EPC) and when referring to a complete cellular system, including both radio access network and core network, as well as other possible entities, such as service related entities, the term Evolved Packet System (EPS) can be used.
As a mere background only, FIG. 1 illustrates an example 3GPP LTE radio communication system 100.
As can be seen, FIG. 1 illustrates a radio access network in an LTE radio communication system 100. In this example, there are two radio network nodes 110a and 110b, each of which is exemplified as an evolved NodeB (eNB). A first eNB 110a is configured to serve one or several UEs, 120a-e, located within the eNB's 100a geographical area of service or the radio cell 130a. The eNB 110a is connectable to a core network (CN). The eNB 110a is also connectable, e.g. via an X2 interface, to a neighboring eNB 110b configured to serve another cell 130b. Accordingly, the second eNB 110b is configured to serve one or several UEs, 120f-j, located within the eNB's 100b geographical area of service or the cell 130b. The eNB 110b is also connectable to a CN.
As is known in the existing art, LTE uses Orthogonal Frequency Division Multiplex (OFDM) in the downlink and DFT-spread OFDM (i.e., DFTS-OFDM, where DFT stands for Discrete Fourier Transform) in the uplink. The basic LTE downlink physical resource can thus be seen as a time-frequency grid as illustrated in FIG. 2, where each resource element corresponds to one OFDM subcarrier during one OFDM symbol interval.
Machine Type Communication (MTC)
A currently popular vision of the future development of the communication in radio communication networks comprises huge numbers of small autonomous devices, which typically, more or less infrequently (e.g., once per week to once per minute) transmit and receive only small amounts of data (or are polled for data). These devices are not assumed to be associated with humans, but may rather be sensors or actuators of different kinds, which may communicate with application servers (which configure the devices and receive data from them) within or outside the cellular network. Hence, this type of communication is often referred to as machine-to-machine (M2M) communication and the devices may be denoted machine devices (MDs). In the 3GPP standardization, the corresponding alternative terms are machine type communication (MTC) and machine type communication devices (MTC devices), with the latter being a subset of the more general term UE. More detailed descriptions of MTC communication can be found in literature, e.g., in the Technical Specification 3GPP TS 22.368 V.13.1.0.
With the nature of MTC devices and their assumed typical uses follow that these MTC devices will often have to be energy efficient, since external power supplies will often not be available and since it is neither practically nor economically feasible to frequently replace or recharge their batteries. In some scenarios, the MTC devices may not even be battery powered, but may instead rely on energy harvesting, e.g. gathering energy from the environment, that is, utilizing (the often limited) energy that may be tapped from sun light, temperature gradients, vibrations, etc. For such energy deprived devices, whose traffic is characterized by relatively small and more or less infrequent transactions (often delay tolerant), it may be important to minimize their energy consumption, e.g. between and in conjunction with the communication events. These MTC devices generally consume energy between the various communication events, e.g. by keeping the radio receiver active to monitor transmissions from the cellular network. Since the periods between the communication events are generally much longer than the actual communication events, this energy consumption may represent a significant part of the overall energy consumption and may even dominate the energy consumption in scenarios where the communication events are infrequent or very infrequent.
Furthermore, MTC may become an important revenue stream for operators and may have a huge potential from the operator perspective. It may be beneficial for operators to be able to serve MTC devices using already deployed radio access technology. Therefore, 3GPP LTE has been investigated as a competitive radio access technology for efficient support of MTC. Lowering the cost of MTC devices may become an important enabler for implementation of the concept of “Internet of things”. Moreover, MTC devices used for many applications may require low operational power consumption and are therefore, as explained earlier, expected to communicate with infrequent small burst transmissions. In addition, there is a substantial market for the M2M use cases of devices deployed inside buildings which would require coverage enhancement in comparison to the defined LTE cell coverage footprint.
For instance, 3GPP LTE Rel-12 has defined a UE power saving mode allowing long battery lifetime and a new UE category allowing reduced modem complexity. In Rel-13, further MTC work is expected to further reduce MTC cost and provide coverage enhancement. A key element to enable cost reduction is to introduce reduced radio frequency (RF) bandwidth of 1.4 MHz in downlink and uplink within any system bandwidth.
EPDCCH (Enhanced Physical Downlink Control Channel)
For regular UEs, the UE may be configured to monitor EPDCCH in addition to PDCCH, see e.g. the Technical Specifications 3GPP TS 36.211 (e.g. Section 6.8A) and 3GPP TS 36.213 (e.g. Section 9.1.4). For each serving cell, higher layer signaling may configure a UE with one or two EPDCCH-PRB-sets (where PRB stands for Physical Resource Block) for EPDCCH monitoring. Each EPDCCH-PRB-set comprises a set of ECCEs (i.e., Enhanced Control Channel Elements) numbered from 0 to NECCE,p,k−1 where NECCE,p,k is the number of ECCEs in EPDCCH-PRB-set p of subframe k. Each EPDCCH-PRB-set may be configured for either localized EPDCCH transmission or distributed EPDCCH transmission.
The UE shall generally monitor a set of EPDCCH candidates on one or more activated serving cells as configured by higher layer signaling for control information, where monitoring implies attempting to decode each of the EPDCCHs in the set according to the monitored DCI (i.e., Downlink Control Information) formats. The set of EPDCCH candidates that should be monitored are defined in terms of EPDCCH UE-specific search spaces. For each serving cell, the subframes in which the UE monitors EPDCCH UE-specific search spaces are configured by higher layers, see e.g. Technical Specification 3GPP TS 36.331.